The present invention relates to an apparatus and method for the manufacture of large transformers, and more particularly to large transformer cores made from strip, ribbon of plates composed of ferromagnetic material, particularly annealed amorphous metal alloys.
Transformers conventionally used in distribution, industrial, power, and dry-type applications are typically of the wound or stack-core variety. Wound core transformers are generally utilized in high volume applications, such as distribution transformers, since the wound core design is conducive to automated, mass production manufacturing techniques. Equipment has been developed to wind a ferromagnetic core strip around and through the window of a pre-formed, multiple turns coil to produce a core and coil assembly. However, the most common manufacturing procedure involves winding or stacking the core independently of the pre-formed coils with which the core will ultimately be linked. The latter arrangement requires that the core be formed with one or more joints for wound core and multiple joints for stack core. Core laminations are separated at those joints to open the core, thereby permitting its insertion into the coil window(s). The core is then closed to remake the joint. This procedure is commonly referred to as xe2x80x9clacingxe2x80x9d the core with a coil.
A typical process for manufacturing a wound core composed of amorphous metal consists of the following steps: ribbon winding, lamination cutting, lamination stacking or lamination winding, annealing, and core edge finishing. The amorphous metal core manufacturing process, including ribbon winding, lamination cutting, lamination relatively complex. Furthermore, in aligning the multiple core limbs, the procedure utilized exerts additional stress on the cores as each core limb is flexed and bent into position. This additional stress tends to increase the core loss resulting in the completed transformer.
The core lamination is brittle from the annealing process and requires extra care, time, and special equipment to open and close the core joints in the transformer assembly process. This is an intrinsic property of the annealed amorphous metal and cannot be avoided. Lamination breakage and flaking is not readily avoidable during this process opening and closing the core joint, but ideally is minimized. The presence of flakes can have broadened detriments to the operation of the transformer. Flakes interspersed between laminar layers can reduce the face-to-face contact of the laminations in a wound core, and also be the cause of electrical short circuits within the core itself, and thus reduce the overall operating efficiency of the transformer. Flakes and the site of a laced joint also reduces the face-to-face contact, reduces the overlap between mating joint sections and again reduces the overall operating efficiency of the transformer. This is particularly important in the locus of the laced joint as it is at this point that the greatest losses are expected to occur due to flaking. Containment methods are required to ensure that the broken flakes do not enter into the coils and create potential short circuit conditions. Stresses induced on the laminations during opening and closing of the core joints oftentimes causes a permanent increase of the core loss and exciting power in the completed transformer, as well as permanent reductions in operating efficiency of the transformer.
Thus, it would be particularly advantageous to the art to provide an improved process for the manufacture of transformers, particularly large transformers having laminated metal cores, especially where such cores are of amorphous metal alloys such as those used in power transformers which improved process inherently features a reduced likelihood of lamination breakage which may occur during the assembly of a power transformer.
It would also be particularly advantageous to provide an improved process for the manufacture of transformers which process comprises reduced handling and manual manipulation steps, and thereby a reduced likelihood of lamination breakage which may occur during the assembly of a power transformer.
It would also be advantageous to provide an annealed amorphous metal core featuring reduced internal stresses and which produced by an improved manufacturing process which includes reduced handling and manual manipulation.
It would also be beneficial to the art to provide a laminated amorphous metal core, particularly three-limbed amorphous metal cores, featuring reduced internal stresses and which produced by an improved manufacturing process which includes reduced handling and manual manipulation.
It is to these and other needs that the present invention is directed.